Identification of the 22-phosphate esters of ecdysone, 2-deoxyecdysone, 20-hydroxyecdysone and 2-deoxy-20-hydroxyecdysone from newly laid eggs of the desert locust, Schistocerca gregaria

Genetic characterization of candidate ecdysteroid kinases in Drosophila melanogaster

Ecdysteroids are major hormones in insects and control molting, growth, reproduction, physiology, and behavior. The biosynthesis of ecdysteroids such as 20-hydroxyecdysone (20E) from dietary sterols is well characterized, but ecdysteroid catabolism is poorly understood. Ecdysteroid kinases (EcKs) mediate the reversible phosphorylation of ecdysteroids, which has been implicated in ecdysteroid recycling during embryogenesis and reproduction in various insects. However, to date, only 2 EcK-encoding genes have been identified, in the silkworm Bombyx mori and the mosquito Anopheles gambiae. Previously, we identified 2 ecdysteroid kinase-like (EcKL) genes-Wallflower (Wall) and Pinkman (pkm)-in the model fruit fly Drosophila melanogaster that are orthologs of the ecdysteroid 22-kinase gene BmEc22K. Here, using gene knockdown, knockout, and misexpression, we explore Wall and pkm's possible functions and genetically test the hypothesis that they encode EcKs. Wall and pkm null mutants are viable and fertile, suggesting that they are not essential for development or reproduction, whereas phenotypes arising from RNAi and somatic CRISPR appear to derive from off-target effects or other artifacts. However, misexpression of Wall results in dramatic phenotypes, including developmental arrest, and defects in trachea, cuticle, and pigmentation. Wall misexpression fails to phenocopy irreversible ecdysteroid catabolism through misexpression of Cyp18a1, suggesting that Wall does not directly inactivate 20E. Additionally, Wall misexpression phenotypes are not attenuated in Cyp18a1 mutants, strongly suggesting that Wall is not an ecdysteroid 26-kinase. We hypothesize that the substrate of Wall in this misexpression experiment and possibly generally is an unknown, atypical ecdysteroid that plays essential roles in Drosophila development, and may highlight aspects of insect endocrinology that are as-yet uncharacterized. We also provide preliminary evidence that CG5644 encodes an ecdysteroid 22-kinase conserved across Diptera.

Phylogenomics of the Ecdysteroid Kinase-like (EcKL) Gene Family in Insects Highlights Roles in Both Steroid Hormone Metabolism and Detoxification

The evolutionary dynamics of large gene families can offer important insights into the functions of their individual members. While the ecdysteroid kinase-like (EcKL) gene family has previously been linked to the metabolism of both steroid molting hormones and xenobiotic toxins, the functions of nearly all EcKL genes are unknown, and there is little information on their evolution across all insects. Here, we perform comprehensive phylogenetic analyses on a manually annotated set of EcKL genes from 140 insect genomes, revealing the gene family is comprised of at least 13 subfamilies that differ in retention and stability. Our results show the only two genes known to encode ecdysteroid kinases belong to different subfamilies and therefore ecdysteroid metabolism functions must be spread throughout the EcKL family. We provide comparative phylogenomic evidence that EcKLs are involved in detoxification across insects, with positive associations between family size and dietary chemical complexity, and we also find similar evidence for the cytochrome P450 and glutathione S-transferase gene families. Unexpectedly, we find that the size of the clade containing a known ecdysteroid kinase is positively associated with host plant taxonomic diversity in Lepidoptera, possibly suggesting multiple functional shifts between hormone and xenobiotic metabolism. Our evolutionary analyses provide hypotheses of function and a robust framework for future experimental studies of the EcKL gene family. They also open promising new avenues for exploring the genomic basis of dietary adaptation in insects, including the classically studied coevolution of butterflies with their host plants.

Twenty-hydroxyecdysone produced by dephosphorylation and ecdysteroidogenesis regulates early embryonic development in the silkmoth, Bombyx mori

Ecdysteroids are key regulators of embryonic development as well as molting and metamorphosis in insects. Although an active form of ecdysteroids, 20-hydroxyecdysone (20E) is known to be produced through ecdysteroidogenesis from cholesterol and dephosphorylation of 20E-phosphate during embryogenesis in Lepidoptera, the importance of these production mechanisms in embryonic development has been unclear. Here, we investigated the activation timing of ecdysteroidogenesis from cholesterol and 20E-phosphate dephosphorylation during early embryogenesis in non-diapause eggs of the silkmoth Bombyx mori by observing morphological development, quantifying 20E and 20E-phosphate, measuring transcripts of enzymes involved in 20E production, and detecting activity of these enzymes using egg extracts. Stage-dependent 20E fluctuation and changes in mRNA amounts of enzymes suggest that the two 20E-producing mechanisms are activated at different stages during embryogenesis. Furthermore, knockdown of a dephosphorylation enzyme delayed development at early embryogenesis, whereas knockdown of an ecdysteroidogenic enzyme delayed development at early-middle embryogenesis. These results suggest that 20E is primarily produced initially by dephosphorylation of 20E-phosphate, and then by ecdysteroidogenesis from cholesterol to induce progression of embryonic development in B. mori.

Genomic and transcriptomic analyses in Drosophila suggest that the ecdysteroid kinase-like (EcKL) gene family encodes the 'detoxification-by-phosphorylation' enzymes of insects

Phosphorylation is a phase II detoxification reaction that, among animals, occurs near exclusively in insects, but the enzymes responsible have never been cloned or otherwise identified. We propose the hypothesis that members of the arthropod-specific ecdysteroid kinase-like (EcKL) gene family encode detoxicative kinases. To test this hypothesis, we annotated the EcKL gene family in 12 species of Drosophila and explored their evolution within the genus. Many ancestral EcKL clades are evolutionarily unstable and have experienced repeated gene gain and loss events, while others are conserved as single-copy orthologs. Leveraging multiple published gene expression datasets from D. melanogaster, and using the cytochrome P450s-a classical detoxification family-as a test case, we demonstrate relationships between xenobiotic induction, detoxification tissue-enriched expression and evolutionary instability in the EcKLs and the P450s. We devised a systematic method for identifying candidate detoxification genes in large gene families that is concordant with experimentally determined functions of P450 genes in D. melanogaster. Applying this method to the EcKLs suggested a significant proportion of these genes play roles in detoxification, and that the EcKLs may constitute a detoxification gene family in insects. Additionally, we estimate that between 11 and 16 uncharacterised D. melanogaster P450s are strong detoxification candidates. Lastly, we also found previously unreported genomic and transcriptomic variation in a number of EcKLs and P450s associated with toxic stress phenotypes using a targeted phenome-wide association study (PheWAS) approach in D. melanogaster, presenting multiple future avenues of research for detoxification genetics in this species.

Synthesis of a novel phosphate analog of 20-hydroxylecdysone with potent hypoglycemic activity

A novel, water-soluble 20-hydroxylecdysono-20,22-phosphoric acid 2 and its sodium salt 3 were designed and synthesized from 20-hydroxylecdysone 1 in six steps and with 67% overall yield. The synthesized phosphoric acid 2 exhibited hypoglycemic activity >40-fold more potent than that of 20-hydroxylecdysone 1 at concentrations between 2 × 10⁻⁷ and 2 × 10⁻⁸ mol/l in a glucose consumption test in HepG2 cells. At a concentration of 2 × 10⁻⁹ mol/l, phosphoric acid 2 was still active, causing a maximum increase in glucose consumption of more than 500%, while 20-hydroxylecdysone 1 was inactive.

Growth-promoting effects of ecdysteroids and juvenile hormone on in vitro development of the larval endoparasitoid, Venturia canescens (Hymenoptera: Ichneumonidae)

We previously reported that lipophorin, fetal bovine serum (FBS), and 20-hydroxyecdysone (20-HE) are essential for the development of the larval endoparasitoid Venturia canescens larvae in vitro. The present study was undertaken to determine the optimal concentrations of those three substances in the MGM-450 medium, and to examine the hormonal effects of ecdysteroids and juvenile hormone (JH) on the development of the parasitoid larvae in vitro. When the culture was started with embryos at the post-germband stage, concentrations of 3 mg/ml of lipophorin and 20% of FBS were most suitable for the development of the parasitoid. The growth-promoting effect of 20-HE increased in a concentration-dependent manner and peaked at a concentration of 1 &mgr;g/ml. Excess concentration led to malformations of the larvae. Three other ecdysteroids, ecdysone, 2-deoxy-20-hydroxyecdysone, and polypodine B had the same effect, although their activity was lower than that of 20-HE. Cholesterol had no effect; most larvae failed to develop. When the medium was supplemented with JH, the duration of the developmental period was significantly shortened, but this hormone was not found to be essential.

Purification and characterisation of haemolymph 3-dehydroecdysone 3 beta-reductase in relation to ecdysteroid biosynthesis in the cotton leafworm Spodoptera littoralis

The in vitro secretion of ecdysteroids from the prothoracic glands of last instar larvae of Spodoptera littoralis was detected and analysed by HPLC-RIA. The primary product was identified as 3-dehydroecdysone (approximately 82%), with lesser amounts of ecdysone (approximately 18%). Interconversion of ecdysone and 3-dehydroecdysone by prothoracic glands was not detectable. 3-Dehydroecdysone 3 beta-reductase activity was demonstrated in the haemolymph. Ecdysone, the endproduct, was characterised by reverse-phase and adsorption HPLC, chemical transformation into ecdysone 2, 3-acetonide, and mass spectrometry. The conditions for optimal activity were determined. The enzyme requires NADPH or NADH as cofactor and Km values for NADPH and NADH were determined to be 0.94 microM, and 22.8 microM, respectively. Investigation of the kinetic properties of the enzyme, using either NADPH or NADH as cofactor, revealed that it exhibits maximal activity at low 3-dehydroecdysone substrate concentrations, with a drastic inhibition of activity at higher concentrations (> 5 microM). The results suggest that the 3-dehydroecdysone 3 beta-reductase has a high-affinity (low Km) binding site for 3-dehydroecdysone substrate, together with a lower-affinity inhibition site. The 3 beta-reductase enzyme was purified to homogeneity using a combination of poly(ethylene glycol) 6000 precipitation and successive FPLC fractionation on Mono-Q, phenyl Superose (twice), and hydroxyapatite columns. The native enzyme was shown to be a monomer with molecular mass of 36 kDa by SDS/PAGE and gel-filtration chromatography. Furthermore, the activity of the enzyme during the last larval instar was found to reach a peak prior to that of the haemolymph ecdysteroid titre, supporting a role for the enzyme in development.

Enzymes of ecdysteroid transformation and inactivation in the midgut of the cotton leafworm, Spodoptera littoralis: properties and developmental profiles

In the midgut cytosol of Lepidoptera, ecdysteroids undergo inactivation by transformation via the 3-dehydro derivative to the corresponding 3-epiecdysteroid (3 alpha-hydroxy) and by phosphate conjugation. The oxygen-dependent oxidase catalyses formation of 3-dehydroecdysteroid, which can be reduced either irreversibly by 3-dehydroecdysone 3 alpha-reductase to 3-epiecdysteroid, or by 3-dehydroecdysone 3 beta-reductase back to the initial ecdysteroid. Furthermore, these ecdysteroids undergo further inactivation by phosphorylation. These ecdysteroid transformations have been investigated in last instar larvae of the cotton leafworm, Spodoptera littoralis. The products of the phosphorylation have been characterized as predominantly ecdysteroid 2-phosphate accompanied by smaller amounts of the corresponding 22-phosphate. The phosphotransferases require Mg2+ and ATP. Whereas the 3-dehydroecdysone 3 alpha-reductase has a clear preference for NADPH rather than NADH, the corresponding 3 beta-reductase markedly favours NADH. The physiological significance of the latter enzyme is unclear. The profiles of the various enzymic activities in dialysed midgut cytosol supplemented with appropriate cofactors were determined throughout the last larval instar. All activities were detectable throughout the instar, but the respective enzymes exhibited maxima at different times. Ecdysone oxidase showed a peak early in the instar, with 3-dehydroecdysone 3 alpha-reductase increasing to a peak as the former activity declined. The 3-dehydroecdysone 3 beta-reductase exhibited peak activity late in the instar, a profile similar to that observed for the corresponding haemolymph enzyme involved in reduction of the 3-dehydroecdysone product of the prothoracic glands to ecdysone. Thus, the significance of the midgut 3 beta-reductase may be related to production of active hormone. Both ecydsteroid 22- and 2-phosphotransferases showed high activities early in the instar and then declined. The physiological significance of the profiles for the ecdysone oxidase, the 3-dehydroecdysone 3 alpha-reductase and phosphotransferases is unclear.

Evidence that Y-organs of the crab Cancer antennarius secrete 3-dehydroecdysone

Y-organs are paired glands in crustaceans that secrete a class of steroid hormones (ecdysteroids) that regulate growth, molting and development. The glandular secretion has been assumed to be solely the ecdysteroid, ecdysone, a polyhydroxylated derivative of cholesterol. We previously reported that Y-organs of a crab (Cancer antennarius) additionally secreted an ecdysteroid that is less polar than ecdysone. Evidence is presented here that the other secretion product is 3-dehydroecdysone (3-dhE). The compound co-chromatographed with authentic 3-dhE in both normal-phase, and reversed-phase, high-performance liquid chromatography. Mass spectrometry of the ecdysteroid gave results consistent with its identity as 3-dhE. The putative 3-dhE was radiolabeled by injecting crabs with [3H]cholesterol and then incubating the Y-organs. The putative [3H]3-dhE secretion was then subjected to chemical reduction. The reaction yielded labeled products that co-chromatographed with authentic ecdysone and 3-epiecdysone. Results of other experiments gave the following results: (1) Putative 3-dhE was not altered (chromatographic criteria) by incubations with snail hydrolases. (2) Putative [3H]3-dhE, added to incubations of Y-organ halves or homogenates, was not significantly converted to ecdysone; also, no conversion was evident after incubation in medium alone in which the hemolymph serum supplement was raised to 50% of the volume. (3) [3H]Ecdysone was not converted to putative 3-dhE in vitro by Y-organ halves or homogenates.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation of apolar ecdysteroid conjugates by ovaries of the house cricket Acheta domesticus in vitro

The newly laid eggs of the house cricket Acheta domesticus contain apolar ecdysteroid conjugates, which we have hypothesized to be ecdysone long-chain fatty acyl esters [Whiting & Dinan (1988) J. Insect Physiol., in the press]. The ovaries of mature adult female A. domesticus in vitro convert [3H]ecdysone into apolar conjugates identical with those found in newly laid eggs. Comparison of the radioactive metabolites produced on incubation of [3H]ecdysone with various organs of adult female A. domesticus in vitro indicate that the fat-body is the major producer of polar ecdysteroid metabolites at this stage of development, whereas the ovaries are the major site of production of apolar metabolites. Apolar metabolites are also produced to a lesser extent by the crop, gut sections and the fat-body. Hydrolysis of radioactive metabolites produced by the ovaries with Helix enzymes releases only [3H]ecdysone, and thus ecdysone is not metabolized before conjugation by the ovaries. Formation of chemical derivatives (acetonide and acetates) of these 3H-labelled apolar conjugates strongly indicates that the position of conjugation is through the hydroxy group at C-22 of ecdysone. Extensive chromatographic analysis of the 3H-labelled apolar metabolites produced by the ovaries by t.l.c. and h.p.l.c. and comparison with authenticated reference compounds have conclusively demonstrated that the conjugates consist of ecdysone esterified at C-22 to a mixture of common long-chain fatty acids. The major fatty acyl esters have been identified and their percentage contribution to the mixture determined: laurate (0.5%), myristate (2.8%), palmitate (25.8%), stearate (8.4%), arachidate (1.0%), oleate (15.7%), linoleate (38.8%) and linolenate (2.1%). In addition there are three minor unidentified peaks, one of which has been tentatively identified as ecdysone 22-palmitoleate (2.6%). Comparison of this percentage composition with the previously published fatty acid composition of A. domesticus haemolymph [Wang & Patton (1969) J. Insect Physiol. 15, 851-860] reveals remarkable similarities, indicating that the acyl transferase(s) forming the conjugates have a broad specificity with regard to the fatty acyl substrate.

Synthesis of apolar ecdysone esters by ovaries of the cockroach Periplaneta americana

Ecdysteroid levels detected by RIA in extracts of mature ovaries from Periplaneta americana increased approximately fourfold (53 +/- 10 to 184 +/- 38 ng/g; +/- SEM, n = 3) on treatment with Helix pomatia "sulphatase" enzymes. HPLC analysis showed that this increase in immunoreactivity resulted from the hydrolysis of six apolar compounds that cochromatographed with the ecdysteroid esters previously shown to be present in newly laid oothecae (A1, A2, A3, A4, A5, and A6; A. J. Slinger, L. N. Dinan, and R. E. Isaac (1986). Insect Biochem. 16 (i), 115-119). Intact ovaries cultured in saline were able to take up [3H]ecdysone from the medium and synthesize ecdysone esters, most of which cochromatographed with immunoreactive peaks from ovaries and oothecae. Crude homogenates and membranes prepared from mature ovaries were also able to esterify ecdysone in vitro. The enzyme activity associated with a high-speed pellet was greatly enhanced by the addition of coenzyme A fatty acyl esters, each reaction resulting in the synthesis of a single major metabolite. The three esters formed on incubating ecdysone with coenzyme A-palmitate, -lineate, and -oleate could be characterized by their retention times on HPLC which were identical to compounds A2, A5, and A6, respectively. These compounds were the three quantitatively important immunoreactive esters found in ovaries and newly laid oothecae. The data presented indicates that ovaries can esterify ecdysone with palmitic, linoleic, and oleic acids and that these apolar derivatives are transferred to the egg. The esters appear to be different from the ecdysone 22-fatty acyl esters that have been isolated from ticks and other insects.

Caenorhabditis elegans: occurrence and metabolism of ecdysteroids in adults and dauer larvae

1. Ecdysteroids were detected in extracts of egg-producing adult Caenorhabditis elegans, in dauer larvae and in dietary bacteria. 2. Similar concentrations of free ecdysteroids were recorded in adults and larvae, although the two life cycle stages differed in their ratio of ecdysone: 20-hydroxyecdysone. 3. Patent adults metabolized [3H]ecdysone into apolar products and putative [3H]ecdysone 22-phosphate.

Metabolism of ecdysteroids during the vitellogenesis of the tick Ornithodoros moubata (Ixodoidea, Argasidae): accumulation of apolar metabolites in the eggs

The fate of injected [3H]ecdysone [( 3H]E) and 20-hydroxy-[3H]ecdysone [( 3H]20E) has been investigated in the female tick Ornithodoros moubata (Murray, 1877; sensu Walton, 1962). When injected into fed mated vitellogenic females, [3H]E is converted into [3H]20E and two apolar classes of metabolites, AP1 and AP2. Injected [3H]20E is directly converted into AP1 and AP2. AP2 is incorporated into the ovaries in a high proportion and at the end of the vitellogenic cycle represents about 25% of the total label recovered from the animal. The fate of labeled hormones injected into virgin females which perform an abortive vitellogenic cycle is quite similar. However, the ovaries incorporated less of the AP2 products. Ovaries of mated females cultured in vitro in the presence of [3H]E are able to produce [3H]20E and AP2. AP2 is incorporated, while [3H]20E is mainly found in the medium. Ovaries of virgin females presented a slower rate of transformation and of incorporation of the label. Labeled AP2 is recovered in freshly laid eggs and AP1 in the females after oviposition. AP1 and AP2 can produce [3H]20E, [3H]E, and other minor polar peaks when submitted to hydrolysis by esterase. It is concluded that the female O. moubata possesses a special enzymatic mechanism for transformation of ecdysteroids into apolar products and for selective incorporation of AP2 into the ovaries. These products are present in the freshly laid eggs and could play a role during embryogenesis.

Isolation and identification of ecdysteroid phosphates and acetylecdysteroid phosphates from developing eggs of the locust, Schistocerca gregaria

Maturing eggs of the desert locust, Schistocerca gregaria, contain a variety of ecdysteroid (insect moulting hormone) conjugates and metabolites, four of which have been previously isolated from polar extracts and identified as ecdysonoic acid, 20-hydroxyecdysonoic acid, 3-acetylecdysone 2-phosphate and ecdysone 2-phosphate. In the present study we have isolated eight additional ecdysteroids from similar late-stage eggs by high-performance liquid chromatography. The 22-phosphate esters of ecdysone, 2-deoxyecdysone, 20-hydroxyecdysone and 2-deoxy-20-hydroxyecdysone, all of which were first identified as ecdysteroid components of newly-laid eggs of S. gregaria, were identified by co-chromatography with authentic compounds and by physicochemical techniques. The remaining compounds were identified as 3-acetyl-20-hydroxyecdysone 2-phosphate, 3-epi-2-deoxyecdysone 3-phosphate, 3-acetylecdysone 22-phosphate and 2-acetylecdysone 22-phosphate by fast atom bombardment mass spectrometry, p.m.r. spectroscopy and analysis of the steroid moieties after enzymic hydrolysis. The latter two compounds, after isolation, are susceptible to nonenzymic acetyl migration and deacetylation to give mixtures of ecdysone 22-phosphate and its 2- and 3-acetate derivatives. The possible role and significance of these ecdysteroid conjugates with respect to the control of hormone titres in insect eggs is discussed.

Isolation and identification of 3-acetylecdysone 2-phosphate, a metabolite of ecdysone, from developing eggs of Schistocerca gregaria

A major ecdysteroid conjugate, which accumulates in the eggs of the desert locust, Schistocerca gregaria, during the later stages of embryogenesis, has been isolated by reversed-phase and anion-exchange high-performance liquid chromatography. Hydrolysis of the conjugate with a crude arylsulphatase preparation from Helix pomatia liberates mainly ecdysone 3-acetate. The compound was identified as 3-acetylecdysone 2-phosphate by phosphate analysis of an acid-hydrolysed sample, fast atom bombardment, electron impact and chemical ionization mass spectrometry and 1H and 13Cn.m.r. spectroscopy. The instability of 3-acetylecdysone 2-phosphate on storage results in the formation of ecdysone 2-phosphate, which was identified by physicochemical techniques. 3-Acetylecdysone 2-phosphate and ecdysone 2-phosphate are less susceptible than ecdysone 22-phosphate to hydrolysis in vitro by an enzyme preparation from S. gregaria embryos. The possible role of 3-acetylecdysone 2-phosphate as an inactive end product of ecdysteroid metabolism is discussed.